1. Field of the Invention
The present invention relates to a microactuator and a method for fabricating the same, and more particularly to a microactuator having a piezoelectric element formed on a substrate to have a desired thickness and patterned using an etching process. The present invention also relates to a method for fabricating such a microactuator.
2. Description of the Prior Art
Typically, a microactuator includes a lower structure including a substrate and a chamber, a piezoelectric element attached to the upper surface of the substrate and adapted to generate a mechanical deformation thereof upon receiving a voltage, and an electrode (electrodes) adapted to transmit the voltage to the piezoelectric element.
In such an actuator having the above mentioned configuration, the piezoelectric element has a property exhibiting a poling phenomenon when an electrical field is applied thereto. In other words, the piezoelectric element exhibits an orientation when an electrical field is applied thereto. When a voltage is repeatedly applied across the piezoelectric element between upper and lower electrodes respectively formed at the upper and lower surfaces of the piezoelectric element, repeated mechanical deformation and recovery of the piezoelectric element occur, thereby causing the piezoelectric element to vibrate.
Since the actuator drives by virtue of an electrical field applied thereto, it is necessary to continuously apply a drive voltage to the actuator for such a driving of the actuator.
A variety of conventional methods are known in association with the manufacture of microactuators.
One method is a method in which a lower electrode is formed on a thin substrate patterned to have an accurate size. The resulting structure is then baked at a temperature of 1,200xc2x0 C. Thereafter, a paste for formation of a piezoelectric element is formed over an exposed surface of the lower electrode, and then baked at a temperature of 1,000xc2x0 C. or more, thereby forming a piezoelectric element. Subsequently, an upper electrode is formed on the piezoelectric element and then baked at a temperature of about 800xc2x0 C. Thus, a microactuator is fabricated.
Another method is a method in which a piezoelectric sheet including a plurality of piezoelectric elements is prepared and then bonded to a metal substrate using a third material. In this case, the resulting piezoelectric plate is subjected to a machining process to simultaneously obtain a plurality of actuators each corresponding to one of the piezoelectric elements. Alternatively, a piezoelectric element machined to have a size corresponding to one actuator is bonded to a metal substrate, thereby obtaining an actuator.
Microactuators fabricated in the above mentioned methods have a cross-sectional structure having vertically extending lateral end surfaces. For this reason, the upper electrode for each actuator can be formed only on the upper surface of the piezoelectric element.
Meanwhile, for an application of a drive voltage or other signals to the actuator, input lines should be connected between the upper electrode and a circuit for supplying the drive voltage and other signals.
In order to connect such input lines to the upper electrode for an application of the drive voltage and other signals, a variety of connection methods have been used. For example, a wire bonding method has been used. Also, a method has been used in which input lines are directly connected to the upper electrode.
In accordance with the method in which input lines are connected to the upper electrode of the actuator using a wire bonding process, pads are formed at both the upper electrode and an insulating layer on a substrate, respectively. Wires are then bonded to the pads, respectively. For this reason, the process used is complex, resulting in a degradation in productivity. Moreover, wires, which are exposed, interfere with a process for coupling a printer head provided with the actuator with a cartridge. In severe cases, a part of such wires may be cut. Accordingly, there are problems of a degradation in reliability in terms of quality and a degradation in durability.
The method for directly connecting input lines to the upper electrode of the actuator is advantageous in that the connecting process is simple because it is unnecessary to form an insulating layer and pads for the connection of the input lines to the upper electrode. In this case, however, pressure and heat generated during the connection of the input lines to the upper electrode are directly applied to the piezoelectric element of the actuator, thereby causing the piezoelectric element to be changed in physical properties. As a result, the resulting product may be damaged.
The direct connection of the input lines to the upper electrode of the actuator may also have an adverse influence on a desired deformation of the actuator occurring in response to an application of a drive voltage to the upper electrode.
The above mentioned conventional methods exhibit a further degradation in productivity and quality in the case using an increased number of actuator cells.
In order to solve the above mentioned problems, the applicant has proposed a microactuator fabrication method which involves the steps of attaching a piezoelectric element having a desired thickness to the upper surface of a substrate, and patterning the piezoelectric element using an etching process, thereby forming a microactuator having a desired piezoelectric element pattern.
FIG. 1 schematically illustrates a method for forming a piezoelectric element using an etching process.
In accordance with the illustrated method, a metal substrate 10 is first prepared. A piezoelectric element 14 is then formed over the prepared substrate 10. The piezoelectric element 14 is then patterned using an etching process. Thereafter, an upper electrode 16 is formed on the patterned piezoelectric element 14.
FIG. 2 schematically illustrates a method for forming a piezoelectric element using an etching process.
In accordance with this method, a metal substrate 20 is first prepared. A lower electrode 22 is then formed over the prepared substrate 20. Thereafter, a piezoelectric element 24 is formed over the lower electrode 22. The piezoelectric element 24 is then patterned using an etching process. An upper electrode 26 is subsequently formed on the patterned piezoelectric element 24.
Where a microactuator is fabricated in accordance with the above mentioned method of FIG. 1 or 2 using an etching process, its piezoelectric element has a cross-sectional structure having, at its lateral ends, an inclined shape instead of a vertical shape. Accordingly, it is possible for the upper electrode to be formed not only on the upper surface of the piezoelectric element, but also on a lateral end surface of the piezoelectric element. In other words, the upper electrode formed on the upper surface of the piezoelectric element can extend to the substrate on which the piezoelectric element is formed.
Where the upper electrode exists not only the upper surface of the piezoelectric element, but also on a lateral end surface of the piezoelectric element, it is possible to connect input lines to the portion of the upper electrode disposed at the lateral end surface of the piezoelectric element. This allows for an easy connection of input lines to the actuator.
However, where the piezoelectric element is etched using a general etching pattern, it may have a non-uniform inclination along its etched lateral end surface. In particular, the piezoelectric element has a sharp inclination at a portion of its lateral end surface near the upper end thereof, so that it has a shape edge.
It is difficult to form an upper electrode on the sharp upper portion of the lateral end surface of the piezoelectric element. For this reason, it is easy for the short circuit to be partially cut at the lateral end surface of the piezoelectric element, as shown in FIG. 3. Thus, it is difficult for the upper electrode to extend completely from the upper surface of the piezoelectric element to the substrate.
The present invention has been made in view of the above mentioned problems, and an object of the invention is to provide a method for fabricating a microactuator, in which a groove is formed at a portion of one lateral end surface of a piezoelectric element where an upper electrode is to exist, thereby allowing the piezoelectric element has a gently inclined etched structure having a gradually decreasing height between the upper electrode and a substrate.
Another object of the invention is to provide an actuator fabricated in accordance with the above mentioned method.
In accordance with one aspect, the present invention provides a microactuator comprising: a substrate; input lines adapted to apply a drive voltage and signals to an upper electrode; a lower electrode formed on an upper surface of said substrate; a piezoelectric element formed on an upper surface of said lower electrode, said piezoelectric element being provided, at a portion to be connected with said input lines, with at least one etched groove to have a gently inclined lateral surface at said portion; and said upper electrode formed over said piezoelectric element in such a fashion that it extends from an upper surface of said piezoelectric element to said gently inclined lateral surface, said upper electrode being connected to said input lines; whereby said connection between said upper electrode and said input lines is improved.
In accordance with another aspect, the present invention provides a microactuator comprising: a metal substrate; input lines adapted to apply a drive voltage and signals to an upper electrode; a piezoelectric element formed on an upper surface of said metal substrate, said piezoelectric element being provided, at a portion to be connected with said input lines, with at least one etched groove to have a gently inclined lateral surface at said portion; and said upper electrode formed over said piezoelectric element in such a fashion that it extends from an upper surface of said piezoelectric element to said gently inclined lateral surface, said upper electrode being connected to said input lines; whereby said connection between said upper electrode and said input lines is improved.
In accordance with another aspect, the present invention provides a method for fabricating a microactuator comprising the steps of: preparing a substrate; forming a lower electrode on an upper surface of said substrate; forming a piezoelectric element on an upper surface of said lower electrode; etching a portion of said piezoelectric element corresponding to a region where said piezoelectric element is to be connected to said input liens, thereby forming a groove in such a fashion that said piezoelectric element has a gently inclined lateral surface at said portion; forming an upper electrode on said piezoelectric element in such a fashion that said upper electrode extends from an upper surface of said piezoelectric element to said gently inclined lateral surface of said piezoelectric element; and connecting input lines to said upper electrode; whereby said connection between said upper electrode and said input lines is improved.
In accordance with another aspect, the present invention provides a method for fabricating a microactuator comprising the steps of: preparing a metal substrate; forming a piezoelectric element on an upper surface of said piezoelectric element; etching a portion of said piezoelectric element corresponding to a region where said piezoelectric element is to be connected to said input liens, thereby forming a groove in such a fashion that said piezoelectric element has a gently inclined lateral surface at said portion; forming an upper electrode on said piezoelectric element in such a fashion that said upper electrode extends from an upper surface of said piezoelectric element to said gently inclined lateral surface of said piezoelectric element; and connecting input lines to said upper electrode; whereby said connection between said upper electrode and said input lines is improved.